1. Field of the Invention
This invention relates to an optical fiber cable. More particularly, the present invention relates to a flame-retardant cable having an excellent flame retardancy and retaining a light-transmitting property of an optical fiber.
2. Description of the Related Art
An inorganic glass optical fiber having an excellent light-transmitting property over a broad wavelength range is known and used as the conventional optical fiber, but the inorganic glass optical fiber is defective in that the processability is poor and the flexural stress is weak. In contrast, a plastic optical fiber has a higher pliability than the glass optical fiber, and has a high processability. Moreover, improvements in the plastic optical fiber-preparing technique have made the light-transmitting distance of the optical fiber long, and thus plastic optical fibers are now utilized as optical fibers for short-distance LAN and light information-transmitting members for various communications. Namely, the range of application for plastic optical fibers has been expanded.
When utilized in various fields, the plastic optical fiber is used in the form of a cable or cord fabricated by covering a single-core or multiple-core optical fiber with a protecting covering material (jacket material), or an optical fiber cable fabricated by combining a optical fiber yarn or an assembly thereof with a tension member or the like.
When a sheet formed by many plastic optical fibers joined in parallel is used, the sheet is covered with a protecting covering material (jacket material) and combined with a tension member or an electric wire.
Materials heretofore used as the protecting covering material for a plastic optical fiber are limited to polyvinyl chloride, polyethylene and the like.
Unlike nonflammable glass fibers, flammable plastic optical fibers are burnt, or dripping occurs when these fibers come into contact with a flame. When the conventional covering material is used, it is difficult to obtain a cable having an excellent flame retardancy from a plastic optical fiber. Moreover, even if a conventional flame-retardant material is used as the covering material, the flame-retardant component migrates into the optical fiber with a lapse of time, and thus the transparency of the fiber per se becomes poor.